In the art of power toothbrushes, particularly acoustic toothbrushes, an important consideration is the cleaning performance (or lack thereof) of the toothbrush in the interproximal spaces of the teeth, i.e. the spaces between two adjacent teeth and/or the spaces between the teeth and the adjoining gum tissue, down into the subgingival areas beneath the gum line. Acoustic-type power toothbrushes generally have had at least some success in cleaning these interproximal spaces, even though they are beyond the physical reach of the brush elements. Cleaning these interproximal spaces is important, since they harbor pathogenic bacteria and in the case of the gums hence prone to the incidence of periodontal disease.
The success of acoustic toothbrushes in effectively cleaning these regions generally depends upon their ability to disrupt the bacteria in the regions by the agitation of a fluid medium which reaches into the regions, producing sufficient instantaneous velocities and pressures therein so as to damage/disrupt the bacteria. The fluid medium, which could be various combinations of dentifrice, water and saliva, is energized so that instantaneous changes in pressure are produced, giving rise to acoustic effects of cavitation and streaming, which are typically evidenced by the formation of small bubbles visible at the ends of the bristles. This can occur at relatively low sonic frequencies, i.e. in the range of 150Hz-1KHz and at amplitudes which are practical in the mouth. An acoustic toothbrush having the required frequency and instantaneous velocity to produce cavitation and streaming effects is disclosed in co-pending application Ser. No. 832,422, titled "High Performance Acoustical Cleaning Apparatus for Teeth," owned by the same assignee as the present invention.
Proper operation of such a toothbrush requires a relatively high efficiency in order to maintain the cavitation effect. Excessive damping of the bristles must be minimized during the actual brushing operation, so that energy can be efficiently transferred to the fluid. In addition, the brushhead must be configured to effectively and efficiently carry fluid as the toothbrush is moved around the mouth by the user, to ensure that there is sufficient fluid in the area of the brushhead to support agitation. This is frequently an important consideration for the upper teeth especially, where there frequently is a reduced saliva environment.
Various aspects of acoustic toothbrushes have been explored by others to improve damping and fluid movement. This invention is particularly directed toward the brushhead configuration, especially as it affects damping, cavitation, streaming and fluid movement.